How can I get that much more vacuum out of my motor. I have a built 454 motor. its a 454 bored .030 over. a xe268 cam and 781 heads with stock size valves and rocker ratio., I don't remember the dome on the piston but it makes it about 10.25 compression ratio. I mud drag with this setup. I have to pull 15 inches at 800 rpm. I'm pulling 13.5 they let me race but it needs pull more vacuum. I've tried adjusting my 4 idle adjustment screws. I'm running my intial timing at 10 degrees. Somebody needs to set me straight on total timing I think I should be checked at about 3000 rpm. Any advice is appreciated. Thanks